Tire wheel

ABSTRACT

A tire wheel, is described, which comprises a tire shell having bead parts, a rim on which the tire shell is supported with the bead parts being pressed against the rim, and a filling material with which the ring-form inner space surrounded by the rim and the tire shell is filled, said filling material having an apparent specific gravity of from 0.08 to 0.3 and an impact resilience of from 50 to 80 (as determined by JIS K-6301) in a free state, consisting of an elastic foam containing butyl rubber or a halogenated butyl rubber and having a closed-cell structure with a water absorption as determined by the water absorption test prescribed in ASTM D1056 of 5% or lower, and being in a compressed state.

This is a Continuation of Application No. 08/580,387 filed Dec. 28,1995.

FIELD OF THE INVENTION

The present invention relates to a tire wheel having a filling materialwith which a inner space surrounded by a rim and a tire shell is filled,i.e., a so-called puncture-free tire. This tire wheel is utilized mainlyin bicycles and the like.

BACKGROUND OF THE INVENTION

Bicycles are used as convenient means of transit. However, the troubleis that commuters or day students may be visited by sudden puncture.Another trouble is that they need to frequently fill air into innertubes. Accordingly, a request of being released from maintenance of tirewheels grows bigger and bigger. Further, there is a growing tendency touse bicycles at a state of emergency such as an earthquake disaster.

Under these circumstances, tire wheels commonly called puncture-freetires have come to be investigated which, for example, comprise a solidtire in place of a tube-containing tire or a tire having a rubber foamwith which the tube-containing part is filled. Structures of such tirewheels have been proposed since long ago. For example, JP-B-U-40-11446,JP-A-47-26476, and JP-A-57-155101 disclose a technique of producing apuncture-free tire wheel by filling the space of a tire body with anelastomer, a soft rubber layer, etc. (The term "JP-B-U" and "JP-A" asused herein mean an "examined Japanese utility model publication" and an"unexamined published Japanese patent application", respectively.)

However, the conventional tire wheels called puncture-free tires have adrawback that the filling material has a large specific gravity (usuallynot smaller than 0.4) and this makes the tire wheels heavy and difficultto handle, although puncture mending can be avoided.

Another drawback of those conventional tire wheels is that because thehardness of the solid rubber or rubber foam is usually as high as 40degrees or higher, the bicycles employing the conventional wheels havepoor shock absorption during riding and hence are uncomfortable to rideon. The hardness of a solid rubber herein means the type A hardnessprescribed in JIS K-6301, while the hardness of a rubber foam hereinmeans the ASKER type C hardness prescribed in Japan Rubber AssociationStandards SRIS-0101.

A further drawback is that since the conventional tires have a lowimpact resilience of lower than 50 (as determined by JIS K-6301), theyhave high rolling resistance and this makes bicycle riding laborious.

Because of the drawbacks described above, those proposed ideas havefailed to be put to wide practical use.

Although a puncture-free tire containing a polyurethane orethylene-propylene-diene rubber (EPDM) sponge fitted into a tire bodyhas, of course, been put to practical use, this sponge-filled tire isstill insufficient in the mitigation of the above-described drawbacksand is inferior to air-filled tires because of these problems. Even ifthe sponge fitted into the inner space of tire body is a closed celltype one, when the sponge is made from a material such as EPDM, airleakage from the closed cells is apt to occur.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a tire wheel which,although having a puncture-free structure, is lightweight andcomfortable to ride on, has low rolling resistance, and can maintainthese performances over long. The tire wheel of this invention thereforeeliminates the problems described above and can be put to wide practicaluse.

The first essential aspect of the present invention resides in a tirewheel comprising a tire shell having bead parts, a rim on which the tireshell is supported with the bead parts being pressed against the rim,and a filling material with which the ring-form inner space surroundedby the rim and the tire shell is filled, said filling material having anapparent specific gravity of from 0.08 to 0.3 and an impact resilienceof from 50 to 80 (as determined by JIS K-6301) in a free state,consisting of an elastic foam containing butyl rubber or a halogenatedbutyl rubber and having a closed-cell structure with a water absorptionas determined by the water absorption test prescribed in ASTM D1056 of5% or lower, and being in a compressed state.

The term "apparent specific gravity" herein means the apparent specificgravity of a filling material which is kept in a free state at theatmospheric pressure without applying any external compressive forcethereto.

The second aspect of the present invention resides in the tire wheelaccording to the first aspect in which the filling material is aring-form elastic foam, and is in a compressed state at a degree ofcompression of from 10% to 50%.

The term "degree of compression" means the percentage of {[(originalvolume)-(volume after compression)]/(volume after compression)}.

The third aspect of the present invention resides in the tire wheelaccording to the first or second aspect in which the surface of thefilling material is covered with cell-free thin rubber layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view illustrating part of a tire wheel having afilling material fitted into the inner space surrounded by a tire shelland a rim.

FIG. 2 is a partly sectional slant view of a semifinished part for thefilling material.

FIG. 3 is a slant view of the filling material.

FIG. 4 is a graph in which tire wheels according to the presentinvention are compared in rolling resistance with an air-filled tire anda tire wheel employing an EPDM filling material.

DETAILED DESCRIPTION OF THE INVENTION

Since the tire wheel according to the present invention contains afilling material fitted into the inner space thereof, which fillingmaterial has an apparent specific gravity of from 0.08 to 0.3 and afree-state impact resilience of from 50 to 80 (as determined by JISK-6301) and consists of an elastic foam, it not only is capable ofsufficiently elastically deforming to shocks, but also is lightweightand has almost satisfactory handleability.

Furthermore, since the filling material is a closed cell elastic foamhaving a water absorption as determined by the water absorption testprescribed in ASTM D1056 of 5% or lower (so-called closed cell typeelastic foam), air leakage is less apt to occur and cushioningproperties are maintained. In particular, in the case where the fillingmaterial used in this invention is an elastic foam containing butylrubber or a halogenated butyl rubber, the tire wheel takes advantage ofthe low gas permeability characteristic of the rubber, so that it canretain over a long period of time the comfortable ride feelingattributable to closed-cell elastic foams.

The term "closed cells" in a foam herein means cells which are separatedby walls and are not interconnected. In contrast to such closed cells,there are cells called "open cells," which means cells interconnectedthrough walls having holes or cells separated by a framework only.

Moreover, since the filling material with which the inner space isfilled is in a compressed state, the gas enclosed in the closed cells iscompressed and this brings about an increased impact resilience andreduced rolling resistance. As a result, the tire wheel comes to havereduced running resistance to provide bicycles which can be ridden onlightly.

The tire wheel according to the second aspect of the invention, in whichthe filling material has been formed beforehand into a ring form so asto fit into the inner space, is free from troubles encountered in thecase of using a filling material obtained by bending a rod-shaped bodyinto a ring form, e.g., free from a gap appearing around the buttedends. In addition, when the filling material fitted into the inner spaceis preferably in a compressed state at a degree of compression of from10% to 50%, moderate hardness is obtained along with satisfactorycushioning properties.

The tire wheel according to the third aspect of the invention, in whichthe surface of the filling material is covered with cell-free thinrubber layer, is almost free from air leakage from the inside of thefilling material and retains air over a long period of use.

(1) Constitution of Tire Wheel

FIGS. 1 to 3 show an embodiment of the tire wheel according to thepresent invention. FIG. 1 is a sectional view illustrating part of thetire wheel having a filling material fitted into the inner spacesurrounded by a tire shell and a rim in a compressed state. FIG. 2 is aslant view of a semi-finished part for the filling material. FIG. 3 is aslant view of the filling material. This embodiment is applied to abicycle tire.

The tire wheel A comprises a tire shell 1, a rim 2, and a fillingmaterial 3 (4).

The tire shell 1 is a rubber tire manufactured through ordinary steps.For example, the tire shell 1 is obtained by thinly covering a cordfabric with a rubber, forming the rubber-covered fabric into a doughnutshape, and forming on the carcass a tread for improving road surfacegripping.

During the steps for forming the tire shell 1, a pair of bead wires 11are disposed in the doughnut having a U-shaped cross section at bothedges thereof, i.e., on both sides of the opening. The bead wires 11 arewound around and fixed to the carcass to thereby serve also to transferthe force generated in the tire to bead parts 1a and then to the rim 2.

The tire shell 1 is supported on the rim 2, with the bead parts 1a beingpressed against the rim 2. This rim 2 is an ordinary product of the sizecorresponding to that of the tire shell 1. When the tire shell 1 isfitted into the rim 2, a ring-form inner space 4 is formed.

The filling material 3 with which this inner space 4 is filled is anelastic foam in a compressed state. The filling material 3, when in afree state at the atmospheric pressure without an external force, has alarger sectional area than the inner space 4. This filling material 3 iscompressed and forcibly fitted into the inner space 4. If a fillingmaterial is merely fitted into the inner space 4 without beingcompressed, gaps result between the filling material 3 and the tireshell 1 because the cross-sectional shape of the inner space 4 is notcompletely the same as that of the filling material 3. As a result, sucha tire has unevenness of cushioning property. In contrast, in the casewhere the filling material 3 is fitted in a compressed state, not onlythe tire is free from such gaps, but also the gas contained in theelastic foam is compressed, resulting in an increased impact resilienceand reduced rolling resistance. Because of the above, the fillingmaterial 3 in a free state has a larger size than the inner space 4.Specifically, the filling material 3 preferably has such a size that itis fitted into the inner space 4 while being compressed at a degree ofcompression of from 10% to 50%. If the degree of compression thereof isbelow 10%, the filling material 3 poorly fits into the tire shell 1,resulting not only in impaired cushioning properties but also in adrawback that the tire shell 1 and the filling material 3 rub againsteach other during running. On the other hand, if the degree ofcompression thereof exceeds 50%, not only it is difficult to fit thefilling material 3 into the tire shell 1, but also the filling material3 becomes too rigid, resulting in impaired cushioning properties and anuncomfortable ride feeling, although the tire has reduced rollingresistance.

The filling material 3 is obtained by molding a rod-shaped body 3ahaving a nearly circular cross section, cutting this semi-finished partinto a proper length, and adhesive-bonding both ends of the cutsemi-finished part to have a ring form corresponding to the tire size.This technique enables mass production of such filling materialscorresponding to various tire sizes.

In this embodiment, the rod-shaped body 3a is obtained by molding andvulcanization in a mold. This production method is advantageous in thatthe filling material obtained has a cell-free thin rubber layer 31 asthe surface coat layer and the cells of the elastic foam are presentonly in the inside 32 (FIG. 2). If cells are present in the surfacelayer, the gas passes off through the cells during long-term use and, asa result, the filling material 3 may lose an impact resilience becauseof drop in pressure. This problem can be eliminated by the thin rubberlayer 31 with which the surface of the filling material is whollycoated. Thus, satisfactory results are obtained. In addition, since bothcut surfaces of the cut rod-shaped body 3a which have exposed cells areadhesive-bonded to each other to form a ring shape, the surface of theresulting filling material is wholly covered with the smooth thin rubberlayer 31 and the gas contained in the elastic foam is prevented frompassing off. In FIG. 1, the thin rubber layer 31 of the filling material3 is not shown.

The filling material 3 consists of an elastic foam containing butylrubber or a halogenated butyl rubber and having a closed-cell structure(a closed-cell type elastic foam) with a water absorption as determinedby the water absorption test prescribed in ASTM D1056 of 5% or lowerwith the exception of the thin rubber layer 31 which is formed on thesurface of the filling material. This filling material 3 is produced by,for example, a method comprising adding a foaming agent, a stabilizer, acrosslinking agent, etc. to a solid comprising butyl rubber or ahalogenated butyl rubber, kneading the mixture, and then heating thekneaded mixture to foam molding, or a method in which a foaming agent, astabilizer, a crosslinking agent, etc. are likewise added to a rubberlatex, and this mixture is cast, foamed and vulcanized, and then dried.

For producing a butyl rubber (including a halogenated butyl rubber)elastomer in which almost 100% of its cells are closed cells, foammolding is carried out by two-stage vulcanization using molds. Thefollowing is a brief explanation of this process.

1) The first vulcanization is conducted in the first mold to a degree ofvulcanization of about from 30 to 50% at a temperature (100-140° C.)lower than the decomposition point of the foaming agent. This stepenables the formation of cell walls which do not break under foamingpressure.

2) The second vulcanization is conducted in the second mold, in whichthe rubber is foamed and simultaneously vulcanized to a degree ofvulcanization of from 90 to 100% at a temperature (150-180° C.) at whichthe foaming agent decomposes. The transfer to the second mold makes itpossible to obtain the desired dimensions.

A representative formulation for a composition for producing the fillingmaterial 3 is shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Representative formulation for filling material                               Ingredient       Parts by weight                                              ______________________________________                                        Rubber ingredient                                                                              100                                                          Vulcanizing agent                                                                              1-3                                                          Vulcanization accelerator                                                                      1-4                                                          Antioxidant      1-3                                                          Foaming agent     4-10                                                        Stabilizer       2-5                                                          Filler           30-50                                                        Plasticizer       0-20                                                        ______________________________________                                    

Examples of the rubber ingredient given in Table 1 include butyl rubberand halogenated butyl rubbers such as brominated and chlorinated butylrubbers. Butyl rubber has low gas permeability, so that the gas enclosedin the closed cells of the elastic foam constituting the fillingmaterial 3 is less apt to pass off and cushioning properties can bemaintained over long. On the other hand, materials other than butylrubber and halogenated butyl rubbers (such as EPDM, natural rubber),although they can form closed cells, are apt to cause gas leakage.Accordingly, when the inner space is filled with the filling materialmade from such a material in a compressed state, the filling material(donut-shaped) becomes thin soon. As the results, an impact resiliencedue to gas can not be obtained.

Moreover, butyl rubber has high shock absorption and is chemicallystable and excellent in weatherability and heat resistance. Hence, butylrubber is suitable for use in a filling material to be fitted intobicycle tires. Brominated butyl rubber and chlorinated butyl rubber notonly have the same advantages as butyl rubber, but are advantageous inthat they can be vulcanized more rapidly than butyl rubber.

Examples of the vulcanization agent include inorganic substances such aspowdery sulfur, colloidal sulfur, and insoluble sulfur. Examples of thevulcanization accelerator include zinc white, magnesium oxide, slakedlime, thiazole compounds such as 2-mercaptobenzothiazole (MBT), dithioicacid salts such as zinc dimethyldithiocarbamate (PZ), and thiuramcompounds such as tetramethylthiuram monosulfide (TMTM). Examples of theantioxidant include trimethyldihydroquinones and phenylenediamine andderivatives thereof. Examples of the foaming agent include inorganicfoaming agents such as ammonium carbonate and sodium bicarbonate andorganic foaming agents such as nitroso compounds, sulfohydrazidecompounds, and azo compounds. Examples of the stabilizer includeinorganic salts such as tribasic lead sulfate, metal soaps such as basiclead stearate, and dibutyltin laurate. Examples of the filler includecarbon black, calcium carbonate, and clay. Examples of the plasticizerinclude DOP, DBP, DIDP, fatty esters, and paraffinic process oils. Thecomposition for use in forming the filling material 3 may furthercontain an ultraviolet absorber, an antistatic agent, a reinforcement,etc.

The filling material 3 in a free state has an apparent specific gravityρ of from 0.08 to 0.30, which is obtained by regulating the expansionratio thereof to from 3.5 to 13.0 by controlling the incorporation of afoaming agent. Consequently, this filling material is considerablylightweight as compared with a commercially available EPDM fillingmaterial of the same size for puncture-free tires, which has an apparentspecific gravity ρ of 0.4 or larger. If the free-state apparent specificgravity ρ of the filling material 3 is below 0.08, this fillingmaterial, even after compressed and fitted into the inner space 4, stillhas a too small apparent specific gravity. As a result, the gas pressurewithin the cells is not increased sufficiently by the compression, sothat the filling material remains soft and has impaired cushioningproperties. For example, a tire wheel containing such a filling materialfitted into its inner space shows almost the same behavior as that of apunctured air-filled tire wheel. On the other hand, if the apparentspecific gravity ρ thereof exceeds 0.30, not only the filling material 3becomes too heavy, but the filling material itself becomes so rigid thatthe tire wheel containing this filling material fitted into its innerspace 4 has impaired cushioning properties. The preferred range of theapparent specific gravity ρ of the filling material is from 0.1 to 0.3.In the case where this filling material 3 is applied to a 26-inchbicycle, the weight of the filling material 3 is from 210 g to 350 g perwheel, so that the proportion of the weight of this filling material inthe weight of the whole bicycle is small. Thus, the tire wheels cancombine a puncture-free function and a small weight.

The filling material 3 described above has a freestate impact resilienceof from 50 to 80 (JIS K-6301). If the impact resilience thereof is lowerthan 50, increased rolling resistance results. If the impact resiliencethereof exceeds 80, the ease of fitting of a tire on a rim is sacrificedand the durability is impaired. With respect to the commerciallyavailable polyurethane or EPDM filling materials for puncture-freetires, their impact resilience in a free state is below 50. In thepresent invention, since the filling material 3 fitted into the innerspace 4 is preferably in a compressed state at a degree of compressionof at least 10% based on its free-state volume, the gas enclosed in theclosed cells is compressed and this brings about a further increasedimpact resilience, as described hereinabove.

The hardness of the filling material 3 in a free state is in the rangeof from 20 degrees to below 40 degrees. This hardness means the ASKERtype C hardness prescribed in Japan Rubber Association StandardsSRIS-0101. If the hardness thereof is lower than 20 degrees, the tirewheel A containing this filling material 3 fitted thereinto is so softthat it not only has the poor cushioning properties, but also hasincreased rolling resistance because of an increased ground contactarea. On the other hand, if the hardness of the filling material 3 is 40degrees or higher, the filling material 3 is so rigid that it shows noshock absorption and has impaired cushioning properties.

Besides the tire shell 1, rim 2, and filling material 3 described above,other components of the tire wheel A include spokes, a hub, and an axle.Such other components are the same as ordinary parts and, hence,explanations thereof are omitted herein.

(2) Performance Test

In order to ascertain the performances of tire wheels A having theabove-described constitution, the tire wheels were examined for ridefeeling, rolling resistance, etc. Three kinds of filling materials 3, α,β, and γ, were used in this test, which were formed according to theformulations shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Formulation for filling material                                              Raw material     α   β  γ                                    ______________________________________                                        Butyl rubber     100       --      --                                         Brominated butyl rubber                                                                        --        100     --                                         Chlorinated butyl rubber                                                                       --        --      100                                        Carbon black     30        30      30                                         P-process oil    10        10      10                                         Zinc white       5         3       3                                          Stearic acid     2         2       2                                          2,2-Methylenebis(4-methyl-                                                                     2         2       2                                          6-t-butylphenol)                                                              Tetramethylthiuram                                                                             1.5       --      --                                         disulfade (TMTD)                                                              Benzothiazyl disulfide (MBTS)                                                                  --        1.0     1.0                                        2-Mercaptobenzothiazole (MBT)                                                                  1         --      --                                         Sulfur           1.5       0.5     0.5                                        Foaming agent, DPT (dinitroso-                                                                 4         4       4                                          pentamethylenepentamine-tetramine)                                            Foaming aid (urea compound)                                                                    4         4       4                                          Total            161.0     156.5   156.5                                      ______________________________________                                    

The tire wheels A used in this test each was a wheel for 26-inchstandard bicycles, and the inner space 4 thereof had a cross-sectionalarea of about 700 mm². The ring-form filling materials 3 each had acircular cross section having a diameter of 35 mm, so that they werecompressed at a degree of compression of about 37%. These fillingmaterials 3 had an apparent specific gravity ρ of 0.11 (Examples 1 to 3)or 0.15 (Examples 4 to 6). These filling materials 3 were compared witha commercially available EPDM filling material (Comparative Example 1)and an air-filled tire (Comparative Example 2). The tire shells 1 andthe rims 2 used were test-use tires and rims produced by InoacCorporation.

Bicycles were actually ridden on to evaluate the ride feeling thereof.As a result, the bicycle employing the air-filled tires and thatemploying the tire wheels containing the filling material 3 having anapparent specific gravity ρ of 0.15 (Examples 4 to 6) gave asatisfactory ride feeling. Table 3 summarizes the results, which aregiven in five grades based on the feeling of the riders (the larger thenumber, the better the property). The standard marks are 3 and thelarger numbers.

Specifically, ten riders played slalom through pylons standing at aninterval of 2 m and then rode across square timbers 3 cm high placed atan interval of 1 m. Each rider evaluated the ride feeling in fivegrades, and the average thereof was rounded.

The bicycles were also evaluated for vibration-absorbing property,controllability, and lightweight property by the same method. Theresults obtained are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Test results                                                                               ρ = 0.11                                                                          ρ = 0.15                                                                            Comp.                                                       Example Example   Example                                                     1   2     3     4   5   6   1    2                               ______________________________________                                        Kind of filling material                                                                     α                                                                             β                                                                              γ                                                                           α                                                                           β                                                                            γ                                                                           --   --                            Ride felling   4     4     4   5   5   5   3    5                             Vibration-absorbing                                                                          4     4     4   5   5   5   3    5                             property                                                                      Controllability                                                                              4     4     4   5   5   5   3    5                             Lightweight property                                                                         5     5     5   4   4   4   2    5                             ______________________________________                                    

Rolling resistance was measured by the following method. Each tire wheelto be tested was pressed against a drum having a diameter of 760 mm, andthe wheel was rotated at a constant rate (30 km/h) while applying a loadof 50 kgf thereto. Thereafter, the driving force which had been appliedto the drum was removed to allow the wheel to run, and the distance overwhich the wheel could run was measured, which distance was converted toa value of rolling resistance. The results obtained are shown in FIG. 4,where the running distance is plotted as abscissa. It was found thatalthough the tire wheels of Examples 1 and 4 according to the presentinvention had slightly higher rolling resistances than the air-filledtire (Comparative Example 2), these tire wheels can be sufficiently putto practical use.

(3) Degree of Compression of Filling Material

Although the inner space 4 is filled with the filling material 3 in acompressed state, the influence of differences in the degree ofcompression on the fitting of tires (tire shells 1 and filling materials3) into rims 2 was examined. As a result, the following were found.

When the degree of compression was 3 or 8%, bead shifting occurred andthe tires were not fitted in their proper position, resulting in anuncomfortable ride feeling. When the degree of compression was 11%, beadshifting did not occur and the tires were satisfactorily fitted. Whenthe degree of compression was 54%, it was very difficult to fit thefilling material 3 into the inner space. When the degree of compressionwas 49%, a sign thereof was shown. As a result of various examinations,a preferred range of the degree of compression is from 10 to 50%, withmore preferred range being from 20 to 40%. As the degree of compressionbecomes smaller than the lower limit of the preferred range, although itbecomes easy to fit the filling material 3 into the inner spacesurrounded by the rim 2 and the tire shell 1, the inner surface of thetire shell and the filling material 3 come to rub against each other andthe thin rubber layer 31 of the filling material may be worn away. Onthe other hand, as the degree of compression becomes greater than theupper limit of the preferred range, it becomes difficult to fit thefilling material 3 into the inner space surrounded by the rim 2 and thetire shell 1.

(4) Apparent Specific Gravity of Filling Material

When the degree of compression of the filling material 3 was set withinthe range from 10 to 50% and the apparent specific gravity ρ of thefilling material 3 varied, the characteristics of the filling materialwith which the inner space 4 of tire wheel is filled was examined. As aresult, the following were found.

The filling material having an apparent specific gravity ρ of 0.07 wastoo soft and had high rolling resistance, making bicycle ridinglaborious. The filling materials having apparent specific gravities ρ of0.11 and 0.15 gave satisfactory results with a comfortable ride feeling.The filling material having an apparent specific gravity of 0.4 showed alow shock-absorbing effect of the compressed gas enclosed in the cells,so that it had a low impact resilience and was unable to absorb shockscaused by road surfaces.

(5) Effects of Examples

According to the tire wheels A of the Examples of this invention, sincethe filling material 3 having cushioning properties is fitted, in acompressed state, into the tire shell 1, the tire shell 1 always retainsan expanded shape due to the filling material 3 and does not suffer apuncture. Namely, because the tire wheels are not of the air-filledtype, the tire shell does not suffer puncturing even when it is piercedwith small holes. As a result, accidents tend to be prevented and thetire wheels A eliminate the necessity of troublesome puncture mending.

As apparent from the results of the performance test, the tire wheels Aare almost comparable to the air-filled tire in that they arelightweight and give a comfortable ride feeling. They have a moderateimpact resilience and a low running resistance, so that bicyclesemploying the tire wheels A can be ridden lightly. Due to butyl rubber,a brominated butyl rubber or a chlorinated butyl rubber contained in theelastic foam, the foam retains its closed-cell structure over long andbuffs shocks caused by road surfaces. Moreover, the bicycles employingthe tire wheels A not only have high controllability with respect tochanging and maintaining directions, but also are lightweight and easilyhandleable.

The present invention is not construed as being limited to theembodiments described above, and various modifications suitable forpurposes and applications can be made within the scope of the invention.Besides the bicycles to which the above embodiments were applied, thepresent invention is also applicable to motor bicycles, carts,agricultural vehicles, wheelchairs, and the like. Although therod-shaped body 3a was formed into a ring shape by adhesive bonding, aring-form filling material 3 can be produced by molding only.

As described above, the tire wheel according to the present inventionnot only enables bicycles to be free from puncturing due to thepuncture-free structure thereof, but also is lightweight, provides acomfortable ride feeling, has low rolling resistance, and can maintainthese performances over long. Consequently, the tire wheel of theinvention is highly effective in improving the quality and performancesof bicycles and in other respects.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A tire wheel comprising a tire shell having beadparts, a rim on which the tire shell is supported with the bead partsbeing pressed against the rim, and a filling material disposed in aring-form inner space surrounded by the rim and the tire shell, saidfilling material having an apparent specific gravity in a free state offrom 0.08 to 0.3 and an impact resilience of from 50 to 80 as determinedby JIS K-6301, in a free state, said filling material consisting of anelastic foam consisting essentially of butyl rubber and having aclosed-cell structure with a water absorption as determined by the waterabsorption test prescribed in ASTM D1056 of 5% or lower, said fillingmaterial being in a compressed state at a degree of compression from 10%to 50%, and said filling material being produced by the steps comprisingconducting a first vulcanization in a first mold at a vulcanization timeat which a degree of vulcanization reaches a range of from 30% to 50%with respect to a vulcanization curve at a temperature lower than adecomposition point of a foaming agent, foaming the rubber thereof at atemperature at which the foaming agent decomposes to conduct a secondvulcanization in a second mold to provide a foamed filling material inwhich substantially 100% of the cells are closed cells, and releasingthe second mold, wherein the foaming agent isdinitroso-pentamethylene-tetramine.
 2. A tire wheel comprising a tireshell having bead parts, a rim on which the tire shell is supported withthe bead parts being pressed against the rim, and a filling materialdisposed in a ring-form inner space surrounded by the rim and the tireshell, said filling material being in a compressed state, said fillingmaterial consisting of an elastic foam consisting essentially of butylrubber, and said filling material being produced by the steps comprisingconducting a first vulcanization in a first mold at a vulcanization timeat which a degree of vulcanization reaches a range of from 30 to 50%with respect to a vulcanization curve at a temperature lower than adecomposition point of a foaming agent, foaming the rubber thereof at atemperature at which the foaming agent decomposes to conduct a secondvulcanization in a second mold to provide a foamed filling material inwhich substantially 100% of the cells are closed cells, and releasingthe second mold, wherein the foaming agent isdinitroso-pentamethylene-tetramine.